1. Field of the Invention
The present invention relates to a method for manufacturing an SOI substrate having a semiconductor layer formed over an insulating film and a method for manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, instead of a bulk silicon wafer, integrated circuits using an SOI (silicon on insulator) substrate have been developed. By utilization of characteristics of a thin silicon wafer formed over an insulating film, semiconductor layers of transistors in the integrated circuit can be electrically separated from each other completely, and further the transistor can be a fully depleted transistor. Thus, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
A SIMOX substrate and a bonded substrate are known as an SOI substrate. For example, an SOI structure of a SIMOX substrate is obtained in such a manner that oxygen ions are implanted into a silicon wafer and heat treatment at greater than or equal to 1300° C. is performed to form a buried oxide (BOX) film, whereby a silicon wafer is formed on a surface of the substrate.
An SOI structure of a bonded substrate is obtained in such a manner that two silicon wafers (a base substrate and a bond substrate) are bonded to each other with an oxide film interposed therebetween and one of the silicon wafers (the bond substrate) is thinned from its rear surface (a surface which is not used for bonding), so that a silicon wafer is formed. Since it is difficult to form a uniform silicon wafer by grinding or polishing, a technique employing hydrogen ion implantation which is called Smart-Cut (registered trademark) has been proposed (e.g., Patent Document 1: Japanese Published Patent Application No. H5-211128).
The summary of the method for manufacturing an SOI substrate will be described below. By implantation of hydrogen ions into a silicon wafer by an ion implantation method, an embrittled region is formed at a predetermined depth from a surface of the silicon wafer. Next, another silicon wafer which serves as a base substrate is oxidized to form a silicon oxide film. After that, the silicon wafer into which hydrogen ions are implanted and the silicon oxide film of the silicon wafer which serves as a base substrate are bonded to each other to bond the two single crystal silicon substrates. Then, through heat treatment, cleavage is caused in the silicon wafer using an ion implanted layer as a cleavage plane, so that a substrate in which a thin single crystal silicon layer is bonded to the silicon wafer which serves as a base substrate is formed.
An ion implantation method is a method in which particles which are desired to be implanted into a sample are ionized in vacuum and accelerated by an electric field to be implanted into the sample. An ion implantation apparatus which is used for an ion implantation method includes an ion source, a mass separation unit, an acceleration unit, a beam operation (electrostatic scan) unit, an implantation chamber (an end station), and an evacuation unit. Further, since a cross section of an ion beam is not uniform, electrical scanning with an ion beam is performed in order to obtain uniformity on a surface of the sample. The implanted particles have a Gaussian distribution in the depth direction.
Further, as an example of a semiconductor device using an SOI substrate, a method for manufacturing a semiconductor device using a substrate with high heat resistance as a supporting substrate, by using Smart-Cut (registered mark) is disclosed (see Patent Document 2: Japanese Published Patent Application No. 2000-012864).